Miniaturization of semiconductor devices and so on has the advantage of achieving improvement in performance and function (high-speed operation, low power consumption, etc.) and reduction in cost and is increasingly accelerated. Such miniaturization is supported by the lithography technology. A transfer mask is one of key techniques, as well as an exposure apparatus and a resist material.
In recent years, development is made of the technology for a 45 nm to 32 nm half-pitch (hereinafter abbreviated to “hp”) generation defined in the semiconductor design rule. The half pitch of 45 nm to 32 nm corresponds to ¼ to ⅙ of the wavelength of 193 nm of ArF excimer laser exposure light. In particular, in the 45 nm hp generation and beyond, only the application of the resolution enhancement technology (RET) such as conventional phase shift technique, oblique-incidence illumination, and pupil filtering, and the optical proximity correction (OPC) has become insufficient. Therefore, the hyper-NA (numerical aperture) technique (immersion lithography) and the double exposure (double patterning) are required.
In the phase shift technique, a predetermined phase difference is given to exposure light transmitted through a phase shift portion. By using the effect of interference of light, a resolution of a transfer pattern is improved.
As a photomask improved in resolution by the phase shift technique, a substrate dug-down type is known in which a quartz substrate is dug down by etching or the like to form a phase shift portion. Also known is another type in which a phase shift film formed on a substrate is patterned to form a phase shift portion.
As the photomask of a substrate dug-down type, there are known a Levenson-type phase shift mask, an enhancer-type phase shift mask, a chromeless phase shift mask, and so on. The chromeless phase shift mask is classified into a type in which a light shielding layer on a line is completely removed and another type (so-called zebra type) in which a light shielding layer on a line is patterned. The Levenson-type phase shift mask or the chromeless phase shift mask of a type in which a light shielding layer in a transfer region is completely removed may be called an alternative phase shifter. In the phase shift mask of this type, 100% of exposure light is transmitted through a phase shift portion. The enhancer-type phase shift mask has a light shielding portion, a transmittance control portion (phase shift of 360°=0°), and a 180° shift portion formed by digging down a glass substrate. In any of the above-mentioned types, a light shielding zone must be formed in a peripheral region (outer peripheral region) along four sides of the photomask (reticle).
As the photomask of the type in which a phase shift portion is formed by patterning a phase shift film formed on a substrate, a halftone phase shift mask or the like is known.